Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -887,6 +887,8 @@
   ScalarEvolution *SE;
   DominatorTree   *DT;
 
+  bool HasGuards;
+
   // Result
   PHINode *WidePhi;
   Instruction *WideInc;
@@ -936,13 +938,14 @@
 public:
   WidenIV(const WideIVInfo &WI, LoopInfo *LInfo,
           ScalarEvolution *SEv, DominatorTree *DTree,
-          SmallVectorImpl<WeakVH> &DI) :
+          SmallVectorImpl<WeakVH> &DI, bool HasGuards) :
     OrigPhi(WI.NarrowIV),
     WideType(WI.WidestNativeType),
     LI(LInfo),
     L(LI->getLoopFor(OrigPhi->getParent())),
     SE(SEv),
     DT(DTree),
+    HasGuards(HasGuards),
     WidePhi(nullptr),
     WideInc(nullptr),
     WideIncExpr(nullptr),
@@ -1584,7 +1587,7 @@
       !NarrowDefRHS->isNonNegative())
     return;
 
-  auto UpdateRangeFromCondition = [&] (Value *Condition) {
+  auto UpdateRangeFromCondition = [&](Value *Condition) {
     CmpInst::Predicate P;
     Value *CmpRHS;
     if (!match(Condition, m_ICmp(P, m_Specific(NarrowDefLHS),
@@ -1600,11 +1603,28 @@
     updatePostIncRangeInfo(NarrowDef, NarrowUser, NarrowDefRange);
   };
 
+  auto UpdateRangeFromGuards = [&](Instruction *Ctx) {
+    if (!HasGuards)
+      return;
+
+    for (BasicBlock::reverse_iterator I = Ctx->getIterator().getReverse(),
+                 E = Ctx->getParent()->rend(); I != E; I++) {
+      Value *Cond = nullptr;
+      if (!match(&*I, m_Intrinsic<Intrinsic::experimental_guard>(
+                 m_Value(Cond))))
+        continue;
+      UpdateRangeFromCondition(Cond);
+    }
+  };
+
+  UpdateRangeFromGuards(NarrowUser);
+
   BasicBlock *NarrowUserBB = NarrowUser->getParent();
   for (auto *DTB = (*DT)[NarrowUserBB]->getIDom();
        L->contains(DTB->getBlock());
        DTB = DTB->getIDom()) {
     auto TI = DTB->getBlock()->getTerminator();
+    UpdateRangeFromGuards(TI);
 
     auto *BI = dyn_cast<BranchInst>(TI);
     if (!BI || !BI->isConditional())
@@ -1688,6 +1708,10 @@
                                        LoopInfo *LI) {
   SmallVector<WideIVInfo, 8> WideIVs;
 
+  auto *GuardDecl = L->getBlocks()[0]->getModule()->getFunction(
+          Intrinsic::getName(Intrinsic::experimental_guard));
+  bool HasGuards = GuardDecl && !GuardDecl->use_empty();
+
   SmallVector<PHINode*, 8> LoopPhis;
   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
     LoopPhis.push_back(cast<PHINode>(I));
@@ -1717,7 +1741,7 @@
     } while(!LoopPhis.empty());
 
     for (; !WideIVs.empty(); WideIVs.pop_back()) {
-      WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts);
+      WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts, HasGuards);
       if (PHINode *WidePhi = Widener.createWideIV(Rewriter)) {
         Changed = true;
         LoopPhis.push_back(WidePhi);
Index: test/Transforms/IndVarSimplify/post-inc-range.ll
===================================================================
--- test/Transforms/IndVarSimplify/post-inc-range.ll
+++ test/Transforms/IndVarSimplify/post-inc-range.ll
@@ -101,3 +101,63 @@
 exit:
   ret void
 }
+
+declare void @llvm.experimental.guard(i1, ...)
+
+define void @test_guard_in_the_same_bb(i32* %base, i32 %limit, i32 %start) {
+; CHECK-LABEL: @test_guard_in_the_same_bb(
+; CHECK-NOT: trunc
+; CHECK-NOT: icmp slt i32
+
+for.body.lr.ph:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ %start, %for.body.lr.ph ], [ %i.inc, %for.inc ]
+  %within_limits = icmp ult i32 %i, 64
+  %i.i64 = zext i32 %i to i64
+  %arrayidx = getelementptr inbounds i32, i32* %base, i64 %i.i64
+  %val = load i32, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:
+  call void(i1, ...) @llvm.experimental.guard(i1 %within_limits) [ "deopt"() ]
+  %i.inc = add nsw nuw i32 %i, 1
+  %cmp = icmp slt i32 %i.inc, %limit
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  br label %exit
+
+exit:
+  ret void
+}
+
+define void @test_guard_in_idom(i32* %base, i32 %limit, i32 %start) {
+; CHECK-LABEL: @test_guard_in_idom(
+; CHECK-NOT: trunc
+; CHECK-NOT: icmp slt i32
+
+for.body.lr.ph:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ %start, %for.body.lr.ph ], [ %i.inc, %for.inc ]
+  %within_limits = icmp ult i32 %i, 64
+  call void(i1, ...) @llvm.experimental.guard(i1 %within_limits) [ "deopt"() ]
+  %i.i64 = zext i32 %i to i64
+  %arrayidx = getelementptr inbounds i32, i32* %base, i64 %i.i64
+  %val = load i32, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:
+  %i.inc = add nsw nuw i32 %i, 1
+  %cmp = icmp slt i32 %i.inc, %limit
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  br label %exit
+
+exit:
+  ret void
+}